A participant of the Olympiad, Kaito was defeated by Ball. Yuria (devil No. 3i - Lucifuge), was taken by Zenom to be placed into the reverse-Kaballah. After the time skip, he had joined forces with Shuri, and
Screenshot 2013-04-07-12-41-34 - Edited

Kaito and his giant knife

the two planned to rescue Yuria and destroy Zenom. Kaito is an OPT who uses weight changing o-parts. Prior to the time skip he used Giant Knife, and uses Heavy Metal, heavy metal is a glove that becomes a suit of armor and kaito can freely change its weight to his will after the time skip when Giant Knife was destroyed.